Antenna system



April 29, 1947.

L. L. LIBBY ANTENNA SYSTEM Filed March 12, 1945 INVENTOR. LESTER L.1/55) BY Aft/7 ATTORNEY Patented Apr. 29, 1947 UNITED; STATES; PATEN TOFFICE? ANTENNA SYSTEM.

Lester L.'. Libby, East range,N.J., assignor to- Federal Telephone andRadio: Corporation, New York, N. Y., a corporation of. DelawareApplication March 12, 1945, Serial No. 582,206

4 Claims.

The present invention-relates to antenna systems particularly ofa theshielded loop type designed to be used over a broad band of the higherfrequencies.

In the copending application of E. Daubaras 1, for Loop antenna systems,Serial No. 478,079, filed March 5, 1943, assigned to Federal Telephoneand Radio Corporation, the assignee of the present application, ashielded loop antenna system is described in which each of a pair ofresistors is connected in series between one end of the loop and abalanced dual transmission line.

These resistors serve to attenuate the effects of undesirable resonancesappearing in the system. In order to maintain the electrical balance orsymmetry of the system and have proper operation, it is essential thatthese two resistors be exactly alike. not only in their resistive valuesbut also in any inherent capacitances and inductances therein. Suchmatching is difficult to obtain, and diflicult to maintain due totemperature variations and variations caused by aging.

An object of the present invention is the provision of an improvedantenna system, particularly of the loop type.

Another object of the present invention is the provision of a loopantenna system in which the resistive means for attenuating the effectsof resonances in the system are mounted in the loop.

Another object of the present invention is the provision of a loopantenna system utilizing resistive means for attenuating the offensiveresonances therein which dispenses with the necessity of matchingresistors.

Other and further objects of the present invention will become apparentand the foregoing will be best understood from the following descriptionof an embodiment thereof, reference being had to the drawing, in which:

Fig. 1 is a diagrammatic view of an antenna system embodying myinvention; and

Fig. 2 is a set of curves used in describing my invention.

In the embodiment of my present invention illustrated in Fig. 1, thenumeral I generally designates a shielded loop antenna having aninner'conductor or antenna loop 2 and a shield 3 having a gap 4 at thetop thereof and being coupled at the lower end thereof to a balanceddual transmission line 5 which is terminated by a terminating resistance6 which may be located within the chassis of a utilization device 1. Theterminated end of this balanced dual transmis- 2. sionline may alsobeconnected-to the primary 8 are transformer9-havingits secondary Inconnected inany suitable manner in thetranslating;

system:

Since the system so far described is in effect a resonant circuit, itwill, as is to be expected, have a resonance peak in its response curve.Moreover, since the resonant circuit is of the transmission line type,it will have more than one of said resonance peaks over a broad band.This is illustrated in Fig. 2 in which relative response is plottedlinearly along the Y axis and frequency is plotted logarithmically alongthe X axis. Curve ll represents the response curve and indicates thetype of peaks that might be obtained in one such system without the useof my invention.

In accordance with my invention, I provide 'a simple means forattenuating these peaks. I ace complish this by providing a resistor l2positioned at the gap and in series with the conductive loop 2. It ispreferred that said resistor I2 have a value of the order of one-half totwo times the surge impedance of the line formed by the inner conductoror antenna loop 2 and the shield 3. Of course it is to be understoodthat this value may be varied, the choice of the value of this resistorbeing made in accordance with a preference between amplitude of responseversus fiatness of response.

Since resistance I2 is arranged at the gap, it is symmetrically disposedin relation to the entire antenna system. Therefore according to mypresent invention matching of resistances which serve to attenuate thepeaks of curve I I no longer is necessary.

Curve l3 represents the improvement over curve II that might be obtainedwith one value of resistance l2. For greater values of resistor thanthat producing curve l3, the response curve will be flatter, but theamplitude of response over the entire range will be less.

While I have described the details of one embodiment of my invention, itwill be apparent that my invention may be used in other embodimentsvarying from that described. For example, while I have described ashielded loop antenna employing my invention, it will be obvious that italso has application to antennas that are not shielded. Furthermore itwill be apparent that the termination of the dual transmission line maybe other than that hereindescribed.

Accordingly, while I have described above the principles of my inventionin connection with specific apparatus, it is to be clearly understoodthat this description is made only by way of example and not as alimitation on the scope of my invention as set forth in the objects ofmy invention and the accompanying claims.

I claim:

1. In an antenna system including a shielded loop antenna said shieldhaving a gap therein, a transmission line coupled at one end to saidloop antenna and terminating means coupled to the other end of saidtransmission line; means for attenuating the effects of resonances insaid system comprising resistive means mounted within said loop antennain series therewith and having a value in the order of one-half to twotimes the surge impedance of the line formed by the loop and its shield.

2. The antenna system according to claim 1 wherein said resistive meansis symmetrically positioned within said loop antenna.

3. In an antenna system including a shielded loop antenna comprising aconductive loop and a shield surrounding said loop and having a gaptherein, a transmission line coupled at one end to said shielded loopantenna, and terminating means coupled to the other end of saidtransmission line; means for attenuating the effects of resonances insaid system comprising a resistor arranged in series with said loop andpositioned at said gap.

4. The antenna system according to claim 3 wherein said resistor has avalue of the order of one-half to two times the surge impedance of theline formed by the loop and its shield.

LESTER L. LIBBY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

